Oxidative stress is imposed on cells as a result of one of three factors: 1) an increase in oxidant generation, 2) a decrease in antioxidant protection, or 3) a failure to repair oxidative damage. Cell damage is induced by reactive oxygen species (ROS). ROS are either free radicals, reactive anions containing oxygen atoms, or molecules containing oxygen atoms that can either produce free radicals or are chemically activated by them. Examples are hydroxyl radical, superoxide, hydrogen peroxide, and peroxynitrite. The main source of ROS in vivo is aerobic respiration, although ROS are also produced by peroxisomal β-oxidation of fatty acids, microsomal cytochrome P450 metabolism of xenobiotic compounds, stimulation of phagocytosis by pathogens or lipopolysaccharides, arginine metabolism, and tissue specific enzymes. Under normal conditions, ROS are cleared from the cell by the action of superoxide dismutase (SOD), catalase, or glutathione (GSH) peroxidase. The main damage to cells results from the ROS-induced alteration of macromolecules such as polyunsaturated fatty acids in membrane lipids, essential proteins, and DNA. Additionally, oxidative stress and ROS have been implicated in disease states, such as Alzheimer's disease, Parkinson's disease, cancer, aging and diabetes.
The formation of peroxide byproducts during the course of normal aerobic metabolism contributes to oxidative stress in living organisms. Peroxides, as well as free radicals derived from them, have been implicated in a variety of degenerative processes and diseases, including inflammation, cardiovascular disease, mutagenesis and cancer, dementia and the aging process. Fortunately, oxidative stress is mitigated by dietary antioxidants, as well as by endogenous enzymes that catalyze the destruction of peroxides and other reactive oxygen species. The latter include glutathione peroxidase (GPx), which promotes the reduction of peroxides with the stoichiometric reductant glutathione (GSH), a tripeptide thiol that is ubiquitous in the cells of higher organisms.
Despite recent therapeutic advances, cardiovascular disease continues to be the leading cause of death among subjects with diabetes. Diabetes-related heart disease makes up the majority of the cardiovascular morbidity and mortality and this pathology results from synergistic interaction amongst various overlapping mechanisms. Diabetes-related heart disease is characterized by a propensity to develop premature, diffuse atherosclerotic disease, structural and functional abnormalities of the microvasculature, autonomic dysfunction and intrinsic myocardial dysfunction (the so-called diabetic ‘cardiomyopathy’, a reversible cardiomyopathy in diabetics that occurs in the absence of coronary atherosclerosis), all of which are exacerbated by hypertension and diabetic nephropathy. As far as the probability of the occurrence of an infarction is concerned, the risk for a diabetic is the same as that for a non-diabetic with a previous infarction.